The short answer is no. In fact, watchmakers are not allowed to make that claim; instead they frequently state that their watches are water resistant.
Water resistance refers to the ability of a watch to withstand water from entering the case. Watches said to be water resistant up to 100 meters are really only suitable for withstanding the "rigors" of rain fall, taking a shower, snorkeling, and shallow-water swimming.
Watches that are water resistant to 300 meters or more are considered safe to scuba-dive with, as they feature sealed case backs, gaskets, and screw-down crowns, which all but eliminate water entry.
Some watches, such as the Rolex Deepsea (pictured above), are so water resistant that it could be argued that they are basically waterproof.